Key switch apparatus

ABSTRACT

A desktop keyboard for data encoders, calculators and the like comprises an electrically insulative board having a plurality of contact members and mounting clusters of normally open key switches to provide electrical engagement between pairs of contact members. An electrically conductive movable bridge member is captured within a key switch housing and pivots in continuous engagement with one staple of a pair while moving into and out of engagement with the second staple of a pair upon predetermined movement of the respective key. A single spring member provides both pretravel and overtravel of each key as well as providing the contact force. The movable contact member is configured in such a way that upon dislodgment from its proper seat caused by an accidental blow, vibration or the like, the contact member is automatically reseated upon actuation of the key. A plurality of multiposition point switches are also mounted on the board and comprise a contact element slidably movable to any one of a plurality of contact members to provide a selected mode of operation.

United States Patent n91 Kravchuck 1 Nov. 25, 1975 1 SWITCH APPARATUS HAVING IMPROVED MEANS FOR SEATING OF MOVABLE CONTRACT MEMBER [75] Inventor: Robert T. Kravchuck, Lincoln, R1.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[22] Filed: July 5, 1973 [2]] Appl. No.1 376,654

[44] Published under the Trial Voluntary Protest Program on January 28, 1975 as document no.

[52] US. Cl 200/159 R; 200/239. 200/275; 200/245 [51] Int. CI. ..H01H 13/52 [58] Field of Search U 200/166 BH, 164 R, 60, 200/159 R, 166 J, 239, 275, 241, 243, 245

[56] References Cited UNITED STATES PATENTS 2,264,955 12/1941 Schellenger 200/164 R 3,707,609 12/1972 Dapot et al. 200/159 8 X Primary Examiner-Robert K. Schaffer Assistant ExaminerWilliam J. Smith Attorney, Agent, or FirmJohn A. Haug; James P. McAndrews; Russell E. Baumann lll [57] ABSTRACT A desktop keyboard for data encoders, calculators and the like comprises an electrically insulative board having a plurality of contact members and mounting clusters of normally open key switches to provide electrical engagement between pairs of contact mem bers. An electrically conductive movable bridge member is captured within a key switch housing and pivots in continuous engagement with one staple of a pair while moving into and out of engagement with the second staple of a pair upon predetermined movement of the respective key. A single spring member provides both pretravcl and overtravel of each key as well as providing the contact force. The movable contact member is configured in such a way that upon dislodgment from its proper seat caused by an accidental blow, vibration or the like, the contact member is automatically reseated upon actuation of the key. A plurality of multiposition point switches are also mounted on the board and comprise a contact element slidably movable to any one of a plurality of contact members to provide a selected mode of operationv 12 Claims, 11 Drawing Figures US. Patent Nov. 25, 1975 Sheet 1 of6 3,922,513

US. Patent Nov. 25, 1975 Sheet 2 of6 3,922,513

US Patent Nov. 25, 1975 Sheet 3 of6 3,922,513

U.S. Patent Nov. 25, 1975 Sheet 4 of6 3,922,513

U.S. Patent Nov. 25, 1975 Sheet 5 of6 3,922,513

US. Patent Nov. 25, 1975 Sheet 6 of6 3,922,513

1 SWITCH APPARATUS HAVING IMPROVED MEANS FOR SEATING OF MOVING CONTACT MEMBER It has been a practice for many years wherever keyboard switches are employed in desktop type apparatus, that is where miniaturization of the switches is not required as in hand held calculators and the like, to provide keys similar to typewriter keys which have significant travel during actuation of the switch and even overtravel after actuation. By depression of a key through most of its stroke, actuation is thus assured. This feature has long since become a required characteristic of such keyboards since operators have become accustomed to it. Such a paratus includes data entry devices, calculators and e like.

It is an object of this invention to provide keyboard apparatus particularly useful with desktop type apparatus in which the keys have substantial travel or stroke. Another object is the provision of such apparatus which is extremely long-lived since it will be subjected to many thousands of cycles. Yet another object is the provision of keyboard switches which are reliable yet relatively inexpensive to produce and are conducive to mass manufacturing techniques; that is the labor content in manufacturing be kept to a minimum. Yet another object is the provision of keyboard apparatus in which contact bounce is minimal.

Another object of the invention is the provision of key switches having a movable contact member with means for automatically seating the contact member should it become dislodged.

Still further objects and advantages of the invention will be apparent from the following detailed description and claims and from the accompanying drawings illustrative of the invention wherein:

FIG. 1 is a perspective view of a keyboard device including a plurality of key switch clusters and a plurality of multiposition point switches mounted on a printed circuit board;

FIG. 2 is a cross sectional view taken on lines 22 of FIG. 1 and showing a key switch in its normally open or contacts disengaged position;

FIG. 3 is a cross sectional view similar to FIG. 2 but showing the key switch in its closed or contacts engaged position;

FIG. 4 is a perspective view of a movable electrically conductive bridge member used in the key switches of FIGS. 1-3;

FIG. 5 is a cross section taken through a portion of the printed circuit board showing a contact element;

FIG. 6 is a cross sectional view similar to FIG. 2 showing the key switch in its normally open position but with the bridge member dislodged from its proper seat;

FIG. 7 is a perspective view of a movable bridge member similar to the member shown in FIG. 4 but configured to provide automatic reseating upon dislodgment thereof;

FIG. 8 is a cross sectional view similar to FIG. 6 but showing the modified movable bridge member;

FIG. 9 is a cross sectional view similar to FIG. 8 but with the key switch in its closed position with the movable bridge member properly seated;

FIG. 10 is a cross sectional plan view taken on lines l010 through multiposition point switch 6 in FIG. I; and

FIG. 11 is a perspective view of the contact arrange ment of the multiposition switch of FIG. 10.

In the detailed description. corresponding reference characters indicate corresponding elements throughout the several view of the drawings.

Briefly, in accordance with the invention an electrically insulative board has a printed circuit disposed on one surface and a plurality of staple like U-shaped members inserted through apertures from the opposed surface with the free ends of the staple legs terminating in electrical contact with selected portions of the printed circuit. A plurality of key clusters are disposed on the printed circuit board each comprising a plurality of key switches, each switch adapted upon depression to electrically engage a pair of staples. Each key switch comprises an elongated keybody mounted for sliding movement in a guideway of a housing toward and away from stationary contacts or staples mounted on the circuit board. An electrically conductive bridge member is captured in the housing and is biased toward bridging electrical engagement between the pair of staples by a coil spring extending from the keybody to the bridge member. The bridge member is provided with a leg having a distal end disposed within an opening formed by a U-shaped portion extending from the keybody. In the preferred embodiment the key switch is normally open since the spring biases the keybody upwardly lift ing the distal end of the bridge member and the bridge member out of engagement with one of the staples of the pair, the bridge member sliding and pivoting on the second staple of the pair. Depression of the switch allows the leg to move down and the bridge member into engagement with one staple of the pair. The contact member is provided with a special configuration so that should the member be dislodged from its proper seat it will automatically be reseated upon actuation of the key.

FIG. 1 shows a Keyboard I particularly useful in desktop calculator models. As seen in the Figure there are a plurality of key clusters 2-5 and a plurality of multiposition point switches 6-8 all of which are mounted on a circuit board 16. Although any conventional circuit board including two sided boards may be employed it is preferred to use a board having desired circuitry printed on one side, the bottom side as viewed in FIG. 1 with the required contacts in the form of staple like members disposed on the opposite side of the board with the legs of the staples extending through apertures in the board and terminating in electrical connection with selected portions of the printed circuitry. It will be realized of course that various other contact members could be employed.

The several key clusters are identical in construction, the only difference being the number of keys and the size of the particular buttons in each cluster. Thus a detailed discussion of one switch will suffice for the others. Key cluster 3 comprises a housing 14 of a conventional electrically insulative material such as polycarbonate mounted on board I6 in any convenient manner as by use of conventional screw fasteners (not shown).

A plurality of key units 12 are formed in housing 14. each unit having a guideway 26 shown in FIGS. 2 and 3. For each key unit 12 a pair of U-shaped electrically conductive contact members in the form of staples 18, are received in apertures provided in electrically in sulative board 16 extending from a first surface 22 to a second opposed surface 24. An elongated keybody 28. also of electrically insulative material is slidingly received in guideway 26 and is adapted for movement toward and away from staples 18, 20. Kcybody 28 is formed with an axially extending slot 30 in communication with a spring receiving bore 32 at the force transmitting end 34 of keybody 28.

An electrically conductive movable bridge member 36, a relatively stiff inflexible member is disposed in a switch chamber 56 within key unit 14. As best seen in FIG. 4, member 36 has two contact sections 38 and 40 with a leg 42 extending from contact section 40 and terminating at a first distal end 44. A second leg 46 extends from contact section 38 and has a second distal end 48. lntermcdiate contact portions 38 and 40 is an upwardly bent portion 50.

Movable bridge member 36 is disposed and captured in a switch chamber with contact section 38 in engage ment with bight 52 of staple 20. A helical coil spring member 58 is also disposed in switch chamber 56 and extends from a spring seat 60 formed by the intersection of slot 30 and bore 32 in keybody 28 to the movable bridge member 36 with the second leg 46 and upwardly bent portion extending into the space defined by spring 58 forming a seat for the spring. Leg 46 cooperates with portion 50 to maintain spring 58 in the desired location. Distal end 48 of leg 46 is provided with a hook portion to facilitate assembly ofthe device. That is. spring 58 can be placed on movable contact member 36 with distal end 48 hooked over the top of the spring maintaining the spring slightly compressed and holding it in position so that it can be easily handied. Once mounted in the switch, distal end 48 is no longer functional since seat 60 of keybody 28 further compresses spring F8 and maintains it away from end 48.

Keybody 28 is formed with a laterally projecting U shaped portion 62 formed by legs 64 (only one being shown) integrally attached to keybody 28 and joined by a bight portion 66. A beveled surface 68 is formed in bight portion 66 which is adapted to engage distal end 44 of leg 42 of movable contact member 36 which is trained through the opening in U-shaped portion 62.

As seen in FIG. 2 in which the switch is in the open position or contacts in the disengaged position, spring 58 reacts against bight S2 and the wall of housing 14 through the extreme end portion 70 of contact section 38 and biases keybody 28 upwardly with bight portion 66 camming leg 42 upwardly lifting contact section 40 out of engagement with bight 54 of staple 18. As the keybody 28 is depressed by a force transmitted through the force transmitting end 72 of the keybody the cam 66 is moved downwardly allowing leg 42 and contact section 40 to move downwardly until contact section 40 comes into engagement with bight S4 of staple 18. Use ofthe single spring 58 as shown provides both pre travel and overtravel of the keybody. It will also be noted that all of the spring force is directly utilized as contact force.

In an exemplary switch made in accordance with the invention the keybody has approximately 0. l 50 inches overall travel (ontact engagement occurs after approximately 0.075 inches followed by 0.075 inches ovcrtravel with surface 66 moving away from distal end 44 and spring 58 being further compressed. While bridge member 36 is pivoting on bight portion 52 of staple 20 there is a slight contact wiping occurring at that section since end forces bridge member 36 to slide slightly to the left as seen in FIGS. 2 and 3, upon contact engagement. However, once contact section 40 comes into engagement with bight 54 there is no further sliding movement and hence no electrical noise after contact engagement.

In certain instances when a key switch is subjected to a blow in a certain direction or possible certain types of vibration it is possible for movable bridge member 36 to become dislodged from its proper seat. As seen in FlG. 6 end 70 can actually be jammed against bight portion 52 of stationary contact 20. Should this happen normal functioning of the switch may be prevented. That is, end 70 may not be freed upon depression of keybody 28 and contact closure (bridging connection between stationary contacts 18 and 20) may not be et fected. In order to avoid this possibility a modified movable bridge member 136 is provided. As seen in FIGS. 7-9 movable bridge member 136 is provided with an outwardly and upwardly curved portion or radius r at distal end 170 and a pivot section 139 which extends downwardly a distance d below contact sections 138, 141).1he remainder of movable bridge memher 136 is essentially identical to bridge member 36 of FIGS. 2-6 including legs 142 and 146 and upwardly bent portion 150 compared to respective portions 42, 46 and 50 of bridge member 36. Pivot section 139 ex tends below contact sections 138. 140 a distance d less than the distance which stationary contacts 18, 20 extend above surface 22 of board 16. Distal end is provided with a sufficiently large radius r so that it readily slides over the surface of bight 52 upon the application of a transverse force or righting moment through coil spring 58 as will be explained below When used with staple like stationary contacts it has been found that reseating is effective when r is at least twice the radius of the staple wire. In determining the optimum distance for r various conditions are considered such as assuming the bight portion 52 itself to be dislocated, either right or left of its desired position or even removed somewhat from surface 22 of board 16.

Should movable bridge member 136 become dislodged, as shown for instance in FIG. 8, with distal end 170 removed from the end of housing 14 and lodged against bight 52 of contact member 20, application of a transverse force to the right as seen in the Figure will cause bridge member 136 to slide to its proper seat. It will be noted that the bottom portion of spring 58 is dis placed to the left as seen in the Figure. As keybody 28 is depressed there is a force moment to the right. as seen in the Figure, the spring attempting to straighten. its longitudinal axis. To aid this force, section 139 acts as the pivot point of a lever raising end 170 near to the top of stationary contact 20. Thus upon depression of keybody 28 end 170 of movable bridge member 136 is caused to slide on bight 52 until end 170 contacts the wall of housing 14 with the bridge member in its proper seat. contact sections 138 and 140 in registration with respective bights 52, 54.

While employment of either radius r or pivot section d is sufficient in many cases to effect automatic reseating use of both sections insures the reseating motion in all cases. The provision of the movable bridge member with downwardly extending section 139 and outwardly and upwardly curved portion 170 has completely obviated the dislodgment problem referred to above by providing automatic reseating upon depression of the key.

Turning now to multiposition point switches 6, 7 and 8 shown in FIG. 1 only one will be discussed in detail since they are of identical construction. In FIG. 6 multiposition point switch 6 is illustrated. The switch is shown having six positions, however the particular number of positions is a matter of choice. Housing 80 mounts a slide member 82 thereon and is formed with opposed lips 84 to confine slide 82 to linear sliding movement (right and left as seen in FIG. 6). Integrally formed with slide member 82 is a knob 86 extending from a raised platform 88 on which a series of serrations 90 is preferably provided to facilitate handling. A series of detents 92 are formed in the bottom surface of slide 82 each being adapted to receive therein a spherical member 94 received in bore 96 formed in housing 80 and biased toward the slide member by a coil spring 98 disposed in bore 96 intermediate member 94 and a bottom wall of the bore forming a spring seat 100.

Grooves 102, 104 are formed on opposite sides of housing 80 on the end of the housing received on printed circuit board 16 and receive therein respective opposite L-shaped tab ends 106, 108 of an electrically conductive retainer plate 110. A bore 112 is formed in slide member 82 and lockingly receives the shank 114 of leg 116 depending from slide member 82. Leg 116 extends through a longitudinally extending slot 118 formed in plate 110 and is received in a slot 120 ofa resilient electrically conductive member 122. Resilient member 122 is generally wave shaped having an undulated convex and concave top and bottom surface. A row of contact members such as staples 126 between outer contact members such as staples 128 and 130 are disposed beneath retainer plate 110 and are arranged so that their bight portions are generally parallel to one another. The legs of staples 126 extend through apertures in board 16 in the same manner as shown in FIG. with at least one leg of staples 126 in electrical connection with a selected portion of the printed circuit. The outer staples 128 and 130 of the row are electrically connected to ends 106, 108 respectively of the retainer plate, however only staple 128 is in electrical connection with the printd circuit. Thus a circuit path can be traced from the printed circuit through staple 128, plate 110, spring contact member 122 to one of the staples 126 depending on the position of slide member 82. The indents 92 are so located relative to the position of staples 126 that when spherical member 94 is received in any one of detents 92 spring contact 122 is biased into electrical contact with one of staples 126.

Housing 82 may be mounted on board 16 in any convenient manner such as by use of screws 132. A duplicate set of detents 134, extend from the center of slide 82 to the right as seen in FIG. 6 so that spherical member 94 and spring 98 can be located either as shown or in bore 136 if so desired.

The design of the keyboard described above is particularly suitable for mass manufacturing techniques. The printed circuit is plated on a surface thereof, the electrical contacts in the form of staples are inserted through apertures provided in the board, the connections are soldered by flow soldering and then the entire board is scrubbed clean with appropriate detergents. The board acts as a support for the several key clusters and multiposition switches which are locked into place,

as mentioned supra, as by use of screw fasteners. No jumpers or other connectors are required so that hand work on the keyboard is kept to an absolute minimum. Once the keyboard is assembled with its switches thereon it is placed in a receiving bezel of a desk top calculator and the circuit board is electrically connected to the other component parts of the apparatus such as for instance, a read only memory (ROM), program counter (PC), instruction register (IR), control decoders and other desired components.

Although the invention has been described with respect to specific preferred embodiments thereof, many variations and modifications will immediately become apparent to those skilled in the art. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.

I claim:

1. A keyboard switch comprising:

an electrically insulative base having opposed first and second surfaces and having a plurality of apertures extending from the first to the second surface;

a pair of electrically conductive generally U-shaped members, each member having two legs joined by a bight portion, each of the legs received in a respective aperture in the base with the bight portion disposed adjacent the first surface, the top of the bights extending a distance d above the first surface;

an elongated keybody having a force receiving end and a force transmitting end;

a housing disposed over the pair of U-shaped members, the housing having guide means and an end wall aligned with the U-shaped members, the keybody received in the guide means and movable therein toward and away from the U-shaped members;

a movable electrically conductive contact bridge member disposed in the housing generally intermediate the U-shaped members and the keybody, the movable contact member having a first free distal end operatively connected to the keybody so that sufficient movement of the keybody away from the U-shaped members lifts at least a portion of the movable contact member away from the U-shaped members, a spring seat formed on the movable contact member;

a coil spring extending from the keybody to the spring seat;

the movable member having first and second contact sections adapted to engage the respective bight portions of the pair of U-shaped members, the movable member having a projection extending downwardly below the first and second contact sections by a distance less than d, the movable member having a second distal end, an outwardly and upwardly curved portion extending from the second distal end adapted to engage the end wall when its normal operating position, whereby upon dislodgement of the movable member from its normal operating position to a position with the second distal end removed from the end wall and located intermediate the pair of U-shaped members the end of the coil spring is displaced away from the end wall so that a righting moment is exerted on the movable member, movement of the keybody toward the U-shaped members increases the righting moment and causes the movable member to slide over the first surface and bight portion of one of the Ushaped members to its normal operating position.

2. A keyboard switch according to claim 1 in which the projection is located intermediate the first and second contact sections.

3. A keyboard switch according to claim 1 in which the spring seat is located intermediate the first and second contact sections.

4. A keyboard switch according to claim 3 in which the projection is located intermediate the spring seat and the contact section adjacent the outwardly and upwardly curved portion.

5. A keyboard switch according to claim 1 in which the radius of the curved portion is at least twice the dis tance the bight portion of the U-shaped members extend above the first surface.

6. A keyboard switch comprising:

an electrically insulative base;

a pair of spaced electrically conductive stationary members supported on and extending a distance d above a surface of the base;

an elongated keybody;

a housing disposed over the pair of stationary members, the housing having guide means and an end wall aligned with the electrically conductive members, the keybody received in the guide means and movable therein toward and away from the members;

a movable electrically conductive contact bridge member disposed in the housing generally intermediate the stationary members and the keybody, the movable contact member having a first free distal end operatively connected to the keybody so that sufficient movement of the keybody away from the stationary members lifts at least a portion of the movable contact member away from the stationary members, a spring seat formed on the movable contact member;

a spring extending from the keybody to the spring seat;

the movable member having first and second contact sections adapted to engage the respective stationary members, the movable member having a projection extending downwardly below the first and second contact sections by a distance less than d, the movable member having a second distal end, an outwardly and upwardly curved portion extending from the second distal end adapted to engage the end wall when in its normal operating position, whereby upon dislodgment of the movable member from its normal operating position to a position with the second distal end removed from the end wall the end of the spring is displaced away from the end wall so that a righting moment is exerted on the movable member, movement of the keybody toward the stationary members increases the righting moment and causes the movable member to slide back to its normal operating position.

7. A keyboard switch according to claim 6 in which the projection is located intermediate the first and sec ond contact sections.

8. A keyboard switch according to claim 6 in which the spring seat is located intermediate the first and second contact sections.

9. A keyboard switch according to claim 8 in which the projection is located intermediate the spring seat 8 and the contact section adjacent the outwardly and upwardly curved portion.

10. A keyboard switch according to claim 6 in which the radius of the curved portion is large relative to distance d.

11. A keyboard switch comprising:

an electrically insulative base;

a pair of spaced electrically conductive stationary members supported on and extending above a surface of the base disposed adjacent the first surface;

an elongated keybody;

a housing disposed over the pair of stationary members, the housing having guide means and an end wall aligned with the electrically conductive members, the keybody received in the guide means and movable therein toward and away from the members;

a movable electrically conductive contact bridge member disposed in the housing generally intermediate the stationary members and the keybody, the movable contact member having a first free distal end operatively connected to the keybody so that sufficient movement of the keybody away from the stationary members lifts at least a portion of the movable contact member away from the stationary members, a spring seat formed on the movable contact member;

a spring extending from the keybody to the spring seat;

the movable member having first and second contact sections adapted to engage the respective stationary members, the movable member having a second distal end, an outwardly and upwardly curved portion extending from the second distal end adapted to engage the end wall when in its normal operating position, the curved portion having a radius which is relatively large relative to distance d, whereby upon dislodgment of the movable member from its normal operating position to a position with the second distal end removed from the end wall the end of the spring is displaced away from the end wall so that a righting moment is exerted on the movable member, movement of the keybody toward the stationary members increases the righting moment and causes the movable member to slide back to its normal operating position.

12. A keyboard switch comprising:

an electrically insulative base having opposed first and second surfaces and having a plurality of apertures extending from the first to the second surface;

a pair of electrically conductive generally U-shaped members, each member having two legs joined by a bight portion, each of the legs received in a respective aperture in the base with the bight portion disposed adjacent the first surface, the top of the bights extending a distance d above the first surface;

an elongated keybody having a force receiving end and a force transmitting end;

a housing disposed over the pair of U-shaped members, the housing having guide means and an end wall aligned with the U-shaped members, the keybody received in the guide means and movable therein toward and away from the U'shaped members;

a movable electrically conductive contact bridge member disposed in the housing generally intermediate the U-shuped members and the keybody, the

a coil spring extending from the keybody to the spring seat;

the movable member having first and second contact sections adapted to engage the respective bight portions of the pair of U-shaped members, the movable member having a second distal end, an outwardly and upwardly curved portion extending from the second distal end adapted to engage the 10 end wall when in its normal operating position, the curved portion having a radius at least twice distance d, whereby upon dislodgment of the movable member from its normal operating position to a position with the second distal end removed from the end wall and located intermediate the pair of U- shaped members the end of the coil spring is displaced away from the end wall so that a righting moment is exerted on the movable member. movement of the keybody toward the U-shaped members increases the righting moment and causes the movable member to slide over the first surface and bight portion of one of the U-shaped members to its normal operating position. 

1. A keyboard switch comprising: an electrically insulative base having opposed first and second surfaces and having a plurality of apertures extending from the first to the second surface; a pair of electrically conductive generally U-shaped members, each member having two legs joined by a bight portion, each of the legs received in a respective aperture in the base with the bight portion disposed adjacent the first surface, the top of the bights extending a distance d above the first surface; an elongated keybody having a force receiving end and a force transmitting end; a housing disposed over the pair of U-shaped members, the housing having guide means and an end wall aligned with the Ushaped members, the keybody received in the guide means and movable therein toward and away from the U-shaped members; a movable electrically conductive contact bridge member disposed in the housing generally intermediate the U-shaped members and the keybody, the movable contact member having a first free distal end operatively connected to the keybody so that sufficient movement of the keybody away from the U-shaped members lifts at least a portion of the movable contact member away from the U-shaped members, a spring seat formed on the movable contact member; a coil spring extending from the keybody to the spring seat; the movable member having first and second contact sections adapted to engage the respective bight portions of the pair of U-shaped members, the movable member having a projection extending downwardly below the first and second contact sections by a distance less than d, the movable member having a second distal end, an outwardly and upwardly curved portion extending from the second distal end adapted to engage the end wall when its normal operating position, whereby upon dislodgement of the movable member from its normal operating position to a position with the second distal end removed from the end wall and located intermediate the pair of U-shaped members the end of the coil spring is displaced away from the end wall so that a righting moment is exerted on the movable member, movement of the keybody toward the U-shaped members increases the righting moment and causes the movable member to slide over the first surface and bight portion of one of the Ushaped members to its normal operating position.
 2. A keyboard switch according to claim 1 in which the projection is located intermediate the first and second contact sections.
 3. A keyboard switch according to claim 1 in which the spring seat is located intermediate the first and second contact sections.
 4. A keyboard switch according to claim 3 in which the projection is located intermediate the spring seat and the contact section adjacent the outwardly and upwardly curved portion.
 5. A keyboard switch according to claim 1 in which the radius of the curved portion is at least twice the distance the bight portion of the U-shaped members extend above the first surface.
 6. A keyboard switch comprising: an electrically insulative base; a pair of spaced electrically conductive stationary members supported on and extending a distance d above a surface of the base; an elongated keybody; a housing disposed over the pair of stationary members, the housing having guide means and an end wall aligned with the electrically conductive members, the keybody received in the guide means and movable therein toward and away from the members; a movable electrically conductive contact bridge member disposed in the housing generally intermediate the stationary members and the keybody, the movable contact member having a first free distal end operatively connected to the keybody so that sufficient movement of the keybody away from the stationary members lifts at least a portion of the movable contact member away from the stationary members, a spring Seat formed on the movable contact member; a spring extending from the keybody to the spring seat; the movable member having first and second contact sections adapted to engage the respective stationary members, the movable member having a projection extending downwardly below the first and second contact sections by a distance less than d, the movable member having a second distal end, an outwardly and upwardly curved portion extending from the second distal end adapted to engage the end wall when in its normal operating position, whereby upon dislodgment of the movable member from its normal operating position to a position with the second distal end removed from the end wall the end of the spring is displaced away from the end wall so that a righting moment is exerted on the movable member, movement of the keybody toward the stationary members increases the righting moment and causes the movable member to slide back to its normal operating position.
 7. A keyboard switch according to claim 6 in which the projection is located intermediate the first and second contact sections.
 8. A keyboard switch according to claim 6 in which the spring seat is located intermediate the first and second contact sections.
 9. A keyboard switch according to claim 8 in which the projection is located intermediate the spring seat and the contact section adjacent the outwardly and upwardly curved portion.
 10. A keyboard switch according to claim 6 in which the radius of the curved portion is large relative to distance d.
 11. A keyboard switch comprising: an electrically insulative base; a pair of spaced electrically conductive stationary members supported on and extending above a surface of the base disposed adjacent the first surface; an elongated keybody; a housing disposed over the pair of stationary members, the housing having guide means and an end wall aligned with the electrically conductive members, the keybody received in the guide means and movable therein toward and away from the members; a movable electrically conductive contact bridge member disposed in the housing generally intermediate the stationary members and the keybody, the movable contact member having a first free distal end operatively connected to the keybody so that sufficient movement of the keybody away from the stationary members lifts at least a portion of the movable contact member away from the stationary members, a spring seat formed on the movable contact member; a spring extending from the keybody to the spring seat; the movable member having first and second contact sections adapted to engage the respective stationary members, the movable member having a second distal end, an outwardly and upwardly curved portion extending from the second distal end adapted to engage the end wall when in its normal operating position, the curved portion having a radius which is relatively large relative to distance d, whereby upon dislodgment of the movable member from its normal operating position to a position with the second distal end removed from the end wall the end of the spring is displaced away from the end wall so that a righting moment is exerted on the movable member, movement of the keybody toward the stationary members increases the righting moment and causes the movable member to slide back to its normal operating position.
 12. A keyboard switch comprising: an electrically insulative base having opposed first and second surfaces and having a plurality of apertures extending from the first to the second surface; a pair of electrically conductive generally U-shaped members, each member having two legs joined by a bight portion, each of the legs received in a respective aperture in the base with the bight portion disposed adjacent the first surface, the top of the bights extending a distance d above the first surface; an elongated keybody having a force receiving end and a force transmitting end; a housiNg disposed over the pair of U-shaped members, the housing having guide means and an end wall aligned with the U-shaped members, the keybody received in the guide means and movable therein toward and away from the U-shaped members; a movable electrically conductive contact bridge member disposed in the housing generally intermediate the U-shaped members and the keybody, the movable contact member having a first free distal end operatively connected to the keybody so that sufficient movement of the keybody away from the U-shaped members lifts at least a portion of the movable contact member away from the U-shaped members, a spring seat formed on the movable contact member; a coil spring extending from the keybody to the spring seat; the movable member having first and second contact sections adapted to engage the respective bight portions of the pair of U-shaped members, the movable member having a second distal end, an outwardly and upwardly curved portion extending from the second distal end adapted to engage the end wall when in its normal operating position, the curved portion having a radius at least twice distance d, whereby upon dislodgment of the movable member from its normal operating position to a position with the second distal end removed from the end wall and located intermediate the pair of U-shaped members the end of the coil spring is displaced away from the end wall so that a righting moment is exerted on the movable member, movement of the keybody toward the U-shaped members increases the righting moment and causes the movable member to slide over the first surface and bight portion of one of the U-shaped members to its normal operating position. 